Alloy steel



March 4, 1941. L. G. sELMl Erm. Y 2234,13()

ALLOY STEEL Filed July 12. 1940 A z3 snaps-sheet 2 A mi. y/W/wm March 4, 1941. L SELMl -rAL 2,234,130

ALLOY STEEL Filed July 12, 1940 5 Sheets-Sheet 3 Patented Mar. 4, l1941 UNITED STATES 2,234,130 vAnnoy STEEL r'nisirrY oFFlCE Luciano G. Selmi, Detroit, and Clarence L. Altenburger, Dearborn," .Mich., assignors to Great Lakes Steel Corporation, Ecorse,

poration of Delaware Mich., a. cor# Application July 12, 1940, Serial No. M5327 3 Claims.

'This invention relates to steel and a composition of'same particularly adapted to rolling into commercial shape of 'varied size and form such that the physical properties of Ithe material of such variable lsizes and forms do not depart appreciably from the optimum values within a range ordinarily covered by that class ofsteel which`has become lmown to the trade as low alloy high tensile steels. 'The invention alsore- 10, lates to a steel of the aforesaid composition capalble of being heat treated in varied shapes and sizes to predetermined but narrow ranges of hardness distributions or other physical properties dependent upon suchhardness distributions.

15 Objects of the invention include the provision of an improved higli tensilesteel; the provision of an improved high tensile steel having a maximum of 0.50% molybdenum; and the provision of an improved high tensile steel having a'maxi- 2o mum of 0.25% carbon.

' Other objects of the invention include a provision for a steel whose composition shall be varlable within denite ranges in accordance with the size and shape of the iinished steel; the pro-l 25 .vision of an improved high tensile steel capable of being heat treated to predetermined but narrow .ranges of hardness distribution or other" physical properties dependent thereon.

' The above being among the objects of the pres 3o ent invention, the same consists in a certain new and useful alloy. steel and particularly to one of new and novel analysis as well as to articles formed therefrom whereby to impart to the same v certain desirable characteristics, to be hereinaft- 35 er describedland then. claimed, having the above.

' and other objects in view.

In the accompanying drawings: Figl is a chart illustrating the properties of the steel of the present invention after. heat.

u treatment:

Fig. 2 is a chart illustrating'the hardness of the steel o'f the present invention across quenched and vtelnpered sections at various drawing teml peratures;

Fig. 3 is a chartl illustrating the hardness at various points through a one-half inchy plate formed ofthe steel of the present invention and which plate hasbeen carburized on one face;l

Fig.A Vi is a photograph of a plate of steel hav- 50 lng an analysis conforming to the present inven tion and having the surface thereof carburlzed and hardened, after having been hit with .3D-cal-y iber standard service bullets l and .30 caliber armor piercing bullets;

.APR 1,4.1942

that shownv in Fig. 4 and ammi-1y carburize'd and anced chemically so as to produce physical' properties within a given range. Such compositions may or may not be capable of. yielding these same -desired properties when subjected to the conditions prevailing in actual commercial steel'manufacturing. Rolling temperatures, rate of coolimg after rolling together with the size and shape of the finished materiaiare the main variables aiiecting this condition.

In the specic case of those steels which have become known to the trade as low-alloy .high

tensile steels, in general they are required to possess tensile properties. approximately as follows:

Yield point 50,000 p.s`.i.'m1n. Tensile strength '10,000 p.s. i. min. Per cent elongation inv2" 25% min.

ble of producing tensile properties in the aforesaid range when rolled hot to comparatively thin gauges, by controllingfinishing temperatures and;

bythe use of copious application ofwater to the steel on the run out table or cooling bed after the steel has passed through' the' last stand-of rolls. Whenthe gauge orthickness of Sifliip or plate, for example, increases, such procedures be come rapidly less eiectiveland tensile properties lower than the 4above Vminima are obtained from the steel in its rolled condition. l

, the past 'few years the requirements of Iow alloy high tensile steels lhave increased swiftly. They were originally intended fos'elatively simweld by all oommercial'welding processes as easily as mild carbon steels; they must be equal to or better than mild canbon steels-1in the matter of y deep drawing objects therefrom;v they must be 'capable of responding to the; ordinary methods of heat treatment and case hardening; they must possess good notched bar resistance at both nor'- malv and sub-normal temperatures, high fatigue resistance, especially fatigue resistance at notches or other stress-raisers which mayvreside vwithin the body of the steel itself. The steel should Many comparatively simple analyses are capaple fabrication methods. Today'such steels must l have all contained nitrogen xed in inactive forms and be free from strain or quench aging. The steel must not be air hardening at any carbon content and should possess no precipitable elements capable of impairing its physical properties upon stress relieving after welding or normalizing. This imposing list of properties demanded by modern steel users is due in'part to the increasing precision of modern manufacturing and partly to the increased use of technical testing of fabricated structures.

A steel, which will hereinafter be referred to as steel A, of the following analysis has been found partly to fulfill the above:

, Percent Carbon .05-.20 Manganese .50-.75 Silicon .'70-.90 AChromium .45-.75 Zirconium .l0-.15 Phosphorus .03 max. Sulphur .03 max.

J `'rile balance is iron and incidental impurities.

' mined but narrow ranges except on small or thin It has been found in accordance with the present invention that a steel, hereinafter referred to as steelv BJ of materially better characteristics thanthe above mentioned steel, adapting it to the same and also to wider and different elds of use, can be obtained .by producing a steel incorporating the same alloying agents as in the steel above -mentioned but containing, in addition thereto,

small amounts of molybdenum, with or without the further addition of small-amounts-of nickel and/orcopper. In other words a steel according to the present invention will A4have the following The nickel and .copper -rnay be-present as residual elements. That is, they may be present in the final steel because of forming an alloying element of the steel scrap employed' in thev production of the Steel ofthe present invention. Where present as residuals nickel may be present in amounts up to approximately 0.10% and copper in amounts up to approximately 0.14%. Amounts ofnickel up to 0.6% .and copper up to 0.3% may occur in the alloy of the present invention without materially'aiecting the properties thereof, thenickel in thehigher 700W- perhaps adding sometoughness, .enhancing the.

- 'on nana, it has beenfnuna that steel heat treatment and-reduction of 'area to a slight extent, and addlng somewhat tof-the ort'osion resisting properties'of the Voy.v However, the

eiects of adding nickel and/or copper up to the maximum percentages noted will not materially affect the principal characteristics of the alloy of the present. invention, and it maybe added or eliminated as desired, and this fact is to be kept in mind in the' following specification and claims regardless of whether these two elements, or either one of them, vis called for or not.

In other words their presence is permissive but not compulsory.

The steel resulting from this analysis, particularly where properly heat treated, will be found to have all of thedesirable attributes or characteristics heretofore listed as required of a steel ofthis-general type under present yday requirements. f

As any example of the effect of added molybdenum onthe'tensile properties of one inch diameter bar rolled with the same procedure on a fourteen vinch merchant mill from 200 ton basic open hearth heats the following -is cited:

As ls evident Vthe tensile strength and yield point are materially raised by the molybdenum addition. l

The effect on the tensile properties after heating to 1600 F. and-air cooling are as follows:

Steel A B 16 69 030 023 51 14 Molyhnnnm 090 Tensile strength p. s i.- 72, 000 83, 000l Yield point p. s. l.- 56,000 61,000 in 2" 1 Y ner cent.- 42 37. 0

Red. aren dn 74 70. 0

steel A B 're` i1estrength. -p.s.l-- '81,000 Yield point..- 57,000 Elongation.- 0 36. 0 Red. area .0 70,0

As evident, steel A has approached very As can be'seen, steel lv has fallen belowtheA minimum requirements whereas steel B is still above them.

In the rolling 'of iiat products onmills-.such as modern high speed `strip mills, it has been composition: s f

L v Per cent nearly the minimum requirements, Upon still Carbon 05-.25 slower cooling as by annealing `from 1600 F. and .Manganese .50-.75 cooling to room temperature with the furnace Silicon .Y0-.90 over a two day period, the following resultsare Chromium .Z4-.'75 obtained: Zirconium .l0-.15

Mo1ybdenum 022.50 '00,01 A 1';- Phosphoru's.. .03 max. v Sulphur .03 max( 000 .75,000 Nickel Up to .6 Optional or 0 50150 Copper Up to .3 }unavoidab1e L "Mft/ g found that steels'of the analyses of steel A 51,500 to 54,500 60,000 te 52,000 45,000 u 49,000

- are affected by flnishingfemperatures as follows 'Y assetto of the analysis of steel BJ the ilnishing ten'lpermV atures may be materially raised without sacricing tensile properties, thereby improving the surface and tolerance of the strip. ,As examples, the following are given.

Finishing temperature 1717 rto 1720 F.

It will be obvious rfrom the foregoing that plate of heavier gauge, can be successfully rolled when vsuch steels of the aforesaid classication fxiontain molybdenum in relatively small proporons.

In the chart shown lin Fig. 1 the response of the steel of the present invention to heat treat ing by quenching and drawing is illustrated by the full line curves and its comparison to the vsteel A of the prior art lacking themolybv denum content is brrfiught out by showing the properties of the latter 'steel under the same conditions hy the dotted linev curves. It will he,

readily understood from these charts that steels of the analyses of thepresent invention are capable of yielding much higher tensile propertie and/or appreciably higher drawing temperatures l c when heat treated than the similar steel A of vso the prior art. Pertinent data is given in Fig. 1 in regard to heat treatmentA procedure which will readily be appreciated by those skilled in the art In the charts'of Fig. 2. hardenability curves of the steel of the present invention taken through a round of one inch diameter i'or various drawing temperatures are shown in full lines and them lcorresponding hardness curves for the similar steel of the. prior art above referred to as steel A are illustrated in comparative relation lint' dotted lines. As will/be readily understood. by those skilled in the artl the curves in Figs. 1 and 2 show that much larger sections of steel having the analyses of the present invention can be successfully heat treated than the steel of the prior analysis A." It might be noted that the steels shown in the charts of Fig. 3' were normalized quenched in water. 'Thereafter they were tem-- pered or drawn for one hour at the temperatures indicated' for the various curvesin Fig. 2, sectioned with a water cooled'rubber wheel, the surface ground smooth on line emery paper and the Rockwell C hardness determined at various distance alongthe radii of the section to v obtain the hardness distributionindicated.

In the matter of carburizlng, it has been foundz that thecase strength atter heat' treating of both steel "A" and steelup to' eomparewith I vthe highest types' of Aalloy steels for carburizlng known to the trade. The core hardness is too low for-many purposes iii-steel PA but steel 3,

condition.

. v due to its greater hardenability, corrects this In the specic case of armer` plate applications, this isa matter ofparamount importance. In such applications, one face of the steel plate to be fabricated into armor plate is carburized. Thereafter, the plate is heat treated. It is requiredthat the face not carburized be not too hard for in that event a bullet striking the car'- burized side may eect cracking on the other side and throw splinters or particles oi thereiromdeeating the purpose of such armor'. On the other hand, if the material of .the plate in regions not carlourized be too soft the case will l Vspall oh when struck by abullet and hence render 15 that area'liable to penetration upon being struck by a second bullet thus defeating the purpose o the armor. Hlustrations oi such spalline; will be observed in the photograph of Fig.'5.

The photographs of Figs. i 4and 5 are those Y .of one-half inch plates carburized in each case to a depth. equal to 25% ci the thicknesses of the plate on .one side 'only and heat treated.- Slices out from the center of the width of the plate gave la distribution of hardness across thel thickness as shown in two cases in Fig. 3. The plate of steel B when struck with a .30 caliber standard service bullet ,for Regular Army Springl eld .30-06rie' at 50 feet showed no penetration' or deformation as shown in the photograph of Fig. 5. In the case of steel A, however, as shown in Fig. 5, the bullets spalled oiI the case of high carbon content in an area around the point of striking oi about one inch diameter as shown. Further, the plate of steel B is not penetrated by armor piercing bullets from the same rifle mentioned herein before at bullet ve- A locities up to 2900'feet per second. In the plat 'of steel ."A'f'the opposite is true.

In the photograph of Fig. 4, the two spots in the upper lefthand corner were produced with ordinaryservice bullets, .the others were produced with armor piercing bullets. In'the photograph of Fig. 5 the two spots in the lower lefthand corner show how the case spelled oif when 4 struck with regular service bullets.

vIt will 'be understood that I do not confine .'uyselfto the speciiic analyses set` forth above.

For many purposes as for instance, heavy plate i where hardnesses in excess Yoi' those shown in the appended charts are required, it will be advantageous to increase both carbon land molybdenum. To attain hardnesses well over 50 Rockwell C in the centers of heavy plate, carbon as high as 0.25% and'xnolybdenum up to 0.50% will be refquired in accordance with the chart shown in 'Fig'. 5, wherein the shaded area covers satisfactory molybdenum ranges at each -plate or other'l sectional thickness. 'l'he lower part of the shaded area is represented by the equation Y rercettMwooott p 1) where "t is thethickness of the plate or thickness of-section in other shapes in inchesandpercent Mo is the percent molybdenum in the steel. Ordinarily plate will preferably have a' composition represented by the top of the shaded area along a line whose equation is.

Y l Percent MoAlO-I-.t-E-M- ;---Q (v2) Rounds on the other hand will 'preferably have a con) f tion approximately in accordance with' It will be appreciated that by. combining the above equations to cover the molybdenum content of a steel within the range-oi the present invention and as indicated in the shaded area, the resulting equation will be:

Thus it win be seen that the thin piategivn yas .2 inch thickness has .02% to'.04% molybdenum Aand this..,amount increases progressively as shown by the black orA shaded area. There the moiybdenummange reads .50% to 1.00% for 5 Yinches thickness-of plate. l

From the foregoing description it will be seen thatthe applicants have produced a-low alloy high tensile steel having its alloy elements selected, combined and balanced within narrow, but speciic and critical ranges, whereby the improved steel having the characteristics and accomplishing the objects set forth is provided. Y

Having thus described our invention, the naturesand scope thereof are defined in the appended claims, it -being understood Ythat the particular relationships and ranges specied Vmay be subject to slight or reasonable variation without departing from the spirit of our invention.

`What is claimed is: l 1. A low alloy, high tensile steel having-properties of-welding by commercial processes, deep drawing, high fatigue resistance and freedom from strain or quench aging, containing 0.05% to 0.25% carbon, 0.50% to 0.75% manganese, 0.70%

to 0.90% silicon, 0.50% to 0.75% chromium, 0.10% to 0.15% zirconium, phosphorus 0.03% maximum, sulphur 0.03% maximum, from a trace ofnickel up to 0.25%, 0.02% to 0.09%'molybdenum, and

all the remainder being iron and incidental imv purities. A

2. A low alloy, high tensile steel having the vproperties of deep drawing characteristics, capable of being welded by commercial processes,

Ahigh fatigue resistance and freedom from strain aging, containing about 0.15% carbon, about l 0.70% manganese, about 0.85% silicon, about 0.50% chromium, about 0.14% zirconium, about 0.09% molybdenum, not over 0.03% phosphorus. not over 0.03% sulphur; not over ,0.6% nickel,

, all the remainder being iron and incidental impurities.

` 3. An article having a sectional thickness meas# ured in inches, and formed of an alloy steel containing iron and incidental impurities, with 0.05% to 0.25% carbon, 0.50% to 0.75% manganese, 

